LINGUIST List 14.1347

Sat May 10 2003

Review: Phonetics: Johnson (2003)

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Johnson, Keith (2003). Acoustic and Auditory Phonetics, 2nd ed.,
Blackwell Publishing.
Announced at http://linguistlist.org/issues/13/13-1449.html
Chao-Yang Lee, Speech Communication Group, Research Laboratory of
Electronics, Massachusetts Institute of Technology
This book is a non-technical introduction to the acoustics of speech.
As the author notes, it covers four major topics:
(1) acoustic properties of major classes of speech sounds,
(2) the acoustic theory of speech production,
(3) the auditory representation of speech and
(4) speech perception.
The target audience is students in introductory courses in linguistic
phonetics, speech and hearing science, and in branches of electrical
engineering and cognitive psychology that deal with speech.
The nine chapters are divided into two parts. The first part presents
the theoretical foundation and signal processing tools for the study
of speech sounds. Chapter 1, basic acoustics and acoustic filters,
introduces the physics of sound: sound propagation, sound waves,
graphical representations of sound, and characteristics of acoustic
filters. Chapter 2 reviews fundamentals of digital signal processing,
explicating how the analog speech signal is converted to digital form
for various types of speech analysis. Chapter 3 discusses the basics
of audition, including the anatomy of the peripheral auditory system,
the sensation of loudness and pitch, and the difference between
acoustic and auditory representations of sound. Chapter 4 on speech
perception is new to the second edition. It illustrates how a speech
perception experiment is conducted by evaluating the perceptual
distance among speech sounds. The role of linguistic background on
speech perception is also demonstrated by a study on Mandarin tone
perception.
Chapter 5, the acoustic theory of speech production, lays the
theoretical foundation for subsequent discussions on the acoustics of
major classes of speech sounds. The voice source and its acoustic
properties, such as fundamental frequency and harmonics, are first
introduced, followed by a discussion on the filtering function of the
vocal tract and its acoustic consequences. The calculation of resonant
frequencies modeled by simple tubes is discussed, so is the estimation
of vowel formant frequencies via the linear predictive coding (LPC).
Based on the acoustic theory presented in Chapter 5, the second part
of the book explicates the acoustic, auditory, and perceptual
characteristics of the major classes of speech sounds. Chapter 6
presents the acoustics of vowels modeled by tubes and by the
perturbation theory. The distribution of vowels in the acoustic vowel
space is discussed with reference to the quantal theory by Stevens and
the theory of adaptive dispersion by Lindblom. The auditory
representation of vowels is compared to the acoustic representation,
followed by a discussion on cross-linguistic vowel perception.
Subsequent chapters on fricatives (Chapter 7), stops and affricates
(Chapter 8), and nasals and laterals (Chapter 9) follow a similar
format of presentation: the acoustic properties, auditory
representations, and perception of the sounds.
Overall, this is an excellent introduction to the acoustics of speech.
In many ways it reminds me of the text by Ladefoged (1996): they are
both compact in size but manage to cover major topics in acoustic
phonetics with a unified theme in an approachable manner. For Johnson
(2003), the overarching theme is to relate the acoustics of speech to
predictions from the acoustic theory of speech production. The
presentation of the acoustic theory is distributed nicely in relevant
chapters (e.g. voicing source and tubes in the chapter on vowels,
noise source in fricatives, and bandwidth in nasals) such that each
chapter is kept concise without sacrificing the depth of
discussion. The author does an admirable job in introducing the
physical basis of speech and acoustic modeling in a non-technical way,
which is particularly helpful for readers who may not have much
mathematical background. The analogies drawn to illustrate key
concepts give the book a user- friendly feel. I also like the
''semi-related stuff in boxes'', explaining in simple terms the
concepts that many of us have always wanted to know but never really
understood well from more technical references.
The emphasis on the role of the auditory and perceptual system is
another attraction of the book. As the author notes, ''the auditory
system warps the speech signal in some very interesting ways, and if
we want to understand the linguistic significance (or lack of it) of
speech acoustics, we must pay attention to the auditory system.'' In
the chapters on major classes of sounds, comparisons are made between
auditory and acoustic representations of speech to alert readers of
the importance of the auditory/perceptual system. Similarly, the role
of linguistic experience in shaping how speech sounds are perceived is
also highlighted with data from cross-linguistic speech perception.
In addition to be used as a supplement to a general phonetics or
speech science text as the author suggests, this book makes a good
companion for a laboratory course in acoustic phonetics. In
particular, the chapter on digital signal processing gives detailed
explanations of how various speech analysis techniques are
derived. This information is particularly useful in how to choose the
appropriate analysis and how to interpret the acoustic data for the
research question. In addition, the chapter on speech perception is a
welcome addition to this new edition. Consistent with the theme that
attention should be paid to the auditory and perceptual side of
phonetics, it illustrates how a perception experiment is designed and
how the results are interpreted.
Since this book is intended as an introductory text, the scope and
depth of coverage is inevitably compromised in exchange for brevity
and readability. It might be helpful to provide a list of suggested
readings for readers wishing to further explore the topics, like what
Pickett (1999) did for example. Furthermore, although this book is
aimed to discuss the acoustic and auditory aspects of phonetics, more
discussion on the articulation of speech seems warranted given that
speech acoustics is mainly a product of speech articulation. It will
complement the theme in relating speech acoustics to modeling from the
acoustic theory of speech production, which is what makes this book
unique.
In sum, if you want to know about the articulatory-acoustic-phonetic
relationships but find Stevens (1998) a little overwhelming, I highly
recommend reading this book first.
REFERENCES:
Ladefoged, P. (1996). Elements of Acoustic Phonetics. The University
of Chicago Press.
Pickett, J. M. (1999). The Acoustics of Speech Communication. Allyn
and Bacon.
Stevens, K. N. (1998). Acoustic Phonetics. MIT Press.
ABOUT THE REVIEWER
Chao-Yang Lee received his graduate training in the cognitive and
linguistic sciences from Brown University. His research interests
include the role of lexical tone in spoken word recognition and the
nature of phonetic categories. He is currently a postdoctoral
associate at MIT and will join the School of Hearing, Speech and
Language Sciences at Ohio University in fall 2003.